First Minister Alex Salmond — the man who could end the United Kingdom — cast his vote near his home in Strichen, Aberdeenshire.

It's time ... a young mother leaves after casting her ballot at Ritchie Hall in Strichen, Scotland.Source: AP

Votes are being cast at 2608 polling places across the country until 10pm local time (7am Friday AEST). The result is expected to take some hours and will most likely be known early on Friday morning local time, around 7am.

Early voting ... it's still dark outside but this voter has already cast his ballot at Ritchie Hall in Strichen. Picture: APSource: AP

Millions are flocking to polling stations across the country for what has been described as a once-in-lifetime chance to vote for independence.

Many arrived early, some before the polling stations opened at 7am (4pm AEST).

In Edinburgh, eager voters formed long lines at polling stations in early-morning light.

Long queues also formed outside polling stations in Glasgow and Ayrshire.

The result is too close to call, with a poll on the eve of the referendum putting the No vote at 51 per cent and Yes at 49 per cent, excluding those voters who are still undecided.

Backing union ... Alistair Darling, leader of the Better Together campaign, and his wife Maggie pose with No campaigners outside the polling station at the Church Hill Theatre in Edinburgh.Source: AP

Scotland's Deputy First Minister Nicola Sturgeon was one of the first to cast her vote, arriving at a Glasgow polling station around 7.30am local time.

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The Yes campaign received a boost when Wimbledon champ Andy Murray, who up to this point has been neutral on the issue, tweeted his support for independence.

Voting No ... former British Prime Minister Gordon Brown visits a polling station at North Queensferry Community Centre. Picture: GettySource: Getty Images

Murray, who is ineligible to vote in the referendum as he lives in England, said he been "swayed by the negativity" of the No campaign and issued a call of duty to his fellow Scots: "Let's do this!"

US President Barack Obama showed where his loyalties lay, tweeting out a message from the White House.

Ballot papers will be counted in each of Scotland's 32 local authority areas after the polling stations close at 10pm local time.

If the Yes side prevails, Salmond will realise a long-held dream of leading his country to independence after an alliance with England formed in 1707.

The United Kingdom teeters on the brink of potentially breaking up, as leaders made last minute appeals to voters on the future of the 300-year-old union amid mass rallies, divided polls and flared tempers.

Faithful to crown ... Unionist protesters in Glasgow make their point during the final day of campaigning. Picture: GettySource: Getty Images

More than four million voters are expected to visit a voting booth, including 124,000 first-time 16 ad 17-year-old voters to answer the simple question of whether Scotland should be an independent nation.

Only a yes or no answer is required but the issue has never been that clear cut and the outcome is expected to be decided by an estimated 400,000 voters who remained undecided up to the moment they entered their local polling booth.

The referendum was described by Salmond as the "most exciting day in Scottish democracy" as he called on voters to "seize the opportunity" and back independence.

He was given a hero's reception as he told a packed rally of 1500 supporters in Perth on the eve of the referendum to continue to appeal to those around them for independence to the moment they case their vote.